1. Field of the Invention
The present invention relates to a rotary plater with radially distributed plating solution and more particularly to a plating solution flow modifier located between an anode and a cathode in a plating cup for increasing the volume of an upward flow of the plating solution toward the cathode with an increase in distance from a center of the plating cup to an outer periphery thereof.
2. Description of the Related Art
Uniform plating thickness is necessary for manufacturing components of a magnetic head. A merged magnetoresistive (MR) head includes a write head portion adjacent a read head portion. The read and write heads are made by thin film technology employing sputter deposition, sputter etching, ion beam milling, photolithography for patterning and plating. The write head includes one or more coil layers embedded in an insulation stack sandwiched between first and second pole pieces. Channel circuitry applies a write signal current to the coil thereby producing a magnetic field in the pole pieces. The one or more coil layers and the first and second pole pieces are typically constructed on a wafer by frame plating. After constructing the first pole piece layer, a first insulation layer and a seedlayer, photoresist is spun on the wafer and then patterned by light exposure and developing to create a shaped opening in the photoresist exposing the seedlayer where copper is to be plated. The wafer is then put in a plater and copper is electroplated on the exposed seedlayer. The photoresist may also have another opening for a test site to measure the thickness of the plated copper. The wafer is then removed from the plater and the photoresist is stripped. Several insulation layers are formed on the coil followed by another seedlayer. Another photoresist layer is spun on the wafer and photopatterned by exposing the photoresist to light and developing. This leaves an opening exposing the seedlayer; the opening has the shape of the second pole piece. The wafer is again placed in the plater and Permalloy (NiFe) is electroplated on the exposed seedlayer. The wafer is then removed from the plater and the photoresist is stripped. Again, another opening may be provided in the photoresist as a test site for measuring the thickness of the plated Permalloy.
A rotary plater for plating the copper and the Permalloy includes a plating bowl for containing a first portion of a plating solution and a substantially circular plating cup located in the plating bowl for containing a second portion of the plating solution. The plating cup has top and bottom portions and a top circular rim that is centered about a vertical axis. A conduit and a pump interconnect the plating bowl to a bottom portion of the plating cup so that the plating solution can be recirculated by transfer from the plating bowl to the bottom portion of the plating cup, then upwardly in the plating cup and over the circular rim back into the plating bowl. An anode is located in the bottom portion of the plating cup and a cathode is located in the top portion of the plating cup. The cathode is capable of supporting a workpiece with a plating surface that faces downwardly so as to receive an upward flow of the plating solution. The workpiece may be a wafer substrate and the plating surface may comprise a plurality of sites for magnetic heads.
In a rotary plater the plating surface rotates relative to the plating solution. Typically the plating surface is rotated. Alternatively, the plating surface is fixed and a paddle rotates below the plating surface to swirl the plating solution around the plating surface. In both instances the plating solution is mixed to insure uniformity of the solution. Unfortunately, the plating solution moves across the plating surface at a velocity that increases with distance from the vertical axis of the plater. This causes a unit volume of the plating solution to be in contact with an outer portion of the plating surface for a shorter time than a unit volume of the plating solution is in contact with an inner portion of the plating surface. Accordingly, less ion exchange takes place between the plating solution and an outer portion of the plating surface than the inner portion of the plating surface. The result is that the plating is thicker on the inner portion of the plating surface. Excessive thickness in the write head decreases the resistance of the writing coil, potentially below a level required for reliable operation of the channel electronics. If plating is used to fabricate a second pole piece for the write head excessive thickness in this element can also change the inductance of the head and cause it to fail to meet the requirements for operation of the channel electronics.
Typical mass production techniques permit hundreds of magnetic heads to be fabricated in rows and columns on a single wafer. With non-uniform plating, the heads near the center of a wafer will be plated more thickly than heads near an outer periphery of the wafer. With the present rotary cup method, about 2% of magnetic heads are discarded at various stages of manufacturing because of thickness non-uniformities caused by presently-available plating technology. Accordingly, there is a need for improving plating uniformity in a rotary cup plater.